To measure particle-dependent parameters, e.g., a particle mass concentration (mass/volume) in exhaust gases and other colloids, scattered light methods are often used. A light beam is emitted into the gas which contains particles. A laser is often used as the light source. The light (scattered light) scattered by the particles is detected and evaluated by at least two sensors positioned at different angles with respect to the direction of the emitted light beam.
The intensity of the scattered light and thus the values of the signals output by the sensors also depend on the average size of the particles in addition to depending on the particle mass concentration to be measured. Therefore, with an unknown particle size, it is impossible to determine the particle mass concentration from the scattered light sensor signals alone.